Electric machines require cooling, in order to remove the heat produced by the losses of the machine and in order to make sure that the temperatures in the machine do not exceed the maximum design temperatures set for the various part of the machine. Those losses are essentially the iron losses of the stator core, the copper losses of the winding, the losses in the rotor, the friction losses in the air gap, and the bearing losses. If the maximum design temperature of the winding is exceeded, there is a risk of a failure in the electrical insulation of the winding wires.
Electric machines designed for a high rotational speed need a more sophisticated cooling system than electric machines designed for more common rotational speeds of for example less than 5,000 min−1, because the losses are produced in a smaller machine volume.
Removing from the machine the amount of heat produced by the losses with high efficiency is an important task because heat removal requires power and therefore is a factor reducing the overall efficiency of the electric machine. A highly sophisticated cooling is a valuable contribution to the high overall efficiency of the electric machine.